/****************************************************************************
 * fs/dirent/fs_opendir.c
 *
 *   Copyright (C) 2007-2009, 2011, 2013-2014, 2017 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>

#include <stdbool.h>
#include <string.h>
#include <dirent.h>
#include <assert.h>
#include <errno.h>

#include <nuttx/kmalloc.h>
#include <nuttx/fs/fs.h>
#include <nuttx/fs/dirent.h>

#include "inode/inode.h"

/****************************************************************************
 * Private Functions
 ****************************************************************************/

/****************************************************************************
 * Name: open_mountpoint
 *
 * Description:
 *   Handle the case where the inode to be opened is within a mountpoint.
 *
 * Inputs:
 *   inode -- the inode of the mountpoint to open
 *   relpath -- the relative path within the mountpoint to open
 *   dir -- the dirent structure to be initialized
 *
 * Return:
 *   On success, OK is returned; Otherwise, a positive errno is returned.
 *
 ****************************************************************************/

#ifndef CONFIG_DISABLE_MOUNTPOINT
static inline int open_mountpoint(FAR struct inode *inode,
                                  FAR const char *relpath,
                                  FAR struct fs_dirent_s *dir)
{
  int ret;

  /* The inode itself as the 'root' of mounted volume.  The actually
   * directory is at relpath into the* mounted filesystem.
   *
   * Verify that the mountpoint inode  supports the opendir() method
   */

  if (!inode->u.i_mops || !inode->u.i_mops->opendir)
    {
       return ENOSYS;
    }

  /* Take reference to the mountpoint inode.  Note that we do not use
   * inode_addref() because we already hold the tree semaphore.
   */

  inode->i_crefs++;

  /* Perform the opendir() operation */

  ret = inode->u.i_mops->opendir(inode, relpath, dir);
  if (ret < 0)
    {
      /* We now need to back off our reference to the inode.  We can't
       * call inode_release() to do that unless we release the tree
       * semaphore.  The following should be safe because:  (1) after the
       * reference count was incremented above it should be >=1 so it should
       * not decrement below zero, and (2) we hold the tree semaphore so no
       * other thread should be able to change the reference count.
       */

      inode->i_crefs--;
      DEBUGASSERT(inode->i_crefs >= 0);

      /* Negate the error value so that it can be used to set errno */

      return -ret;
    }

  return OK;
}
#endif

/****************************************************************************
 * Name: open_pseudodir
 *
 * Description:
 *   Handle the case where the inode to be opened is within the top-level
 *   pseudo-file system.
 *
 * Inputs:
 *   inode -- the inode of the mountpoint to open
 *   dir -- the dirent structure to be initialized
 *
 * Return:
 *   None
 *
 ****************************************************************************/

static void open_pseudodir(FAR struct inode *inode, FAR struct fs_dirent_s *dir)
{
  /* We have a valid pseudo-filesystem node.  Take two references on the
   * inode -- one for the parent (fd_root) and one for the child (fd_next).
   * Note that we do not call inode_addref because we are holding the tree
   * semaphore and that would result in deadlock.
   */

  inode->i_crefs       += 2;
  dir->fd_root          = inode; /* Save the inode where we start */
  dir->u.pseudo.fd_next = inode; /* This is the next node to use for readdir() */

  /* Flag the inode as belonging to the pseudo-filesystem */

#ifndef CONFIG_DISABLE_MOUNTPOINT
  DIRENT_SETPSEUDONODE(dir->fd_flags);
#endif
}

/****************************************************************************
 * Name: open_emptydir
 *
 * Description:
 *   Handle the case where the inode to be opened is an empty, directory node
 *   within the top-level pseudo-file system.  That is, it has no operations
 *   and, therefore, it must be a directory node.  But is has no children
 *   to be enumerated either.
 *
 * Inputs:
 *   dir -- the dirent structure to be initialized
 *
 * Return:
 *   None
 *
 ****************************************************************************/

static inline void open_emptydir(FAR struct fs_dirent_s *dir)
{
  /* We have a valid, but empty pseudo-filesystem node.  fd_next is NULL
   * meaning that we are already at the end of the list of its children.
   * fd_root is NULL so that if the directory is rewound, it will still be
   * at the end of the list.
   */

#if 0 /* Already nullified by kumm_zalloc */
  dir->fd_root          = NULL; /* Save the inode where we start */
  dir->u.pseudo.fd_next = NULL; /* We are at the end of the list */
#endif

  /* Flag the inode as belonging to the pseudo-filesystem */

#ifndef CONFIG_DISABLE_MOUNTPOINT
  DIRENT_SETPSEUDONODE(dir->fd_flags);
#endif
}

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: opendir
 *
 * Description:
 *   The  opendir() function opens a directory stream corresponding to the
 *   directory name, and returns a pointer to the directory stream. The
 *   stream is positioned at the first entry in the directory.
 *
 * Inputs:
 *   path -- the directory to open
 *
 * Return:
 *   The opendir() function returns a pointer to the directory stream.  On
 *   error, NULL is returned, and errno is set appropriately.
 *
 *   EACCES  - Permission denied.
 *   EMFILE  - Too many file descriptors in use by process.
 *   ENFILE  - Too many files are currently open in the
 *             system.
 *   ENOENT  - Directory does not exist, or name is an empty
 *             string.
 *   ENOMEM  - Insufficient memory to complete the operation.
 *   ENOTDIR - 'path' is not a directory.
 *
 ****************************************************************************/

FAR DIR *opendir(FAR const char *path)
{
  FAR struct inode *inode = NULL;
  FAR struct fs_dirent_s *dir;
  struct inode_search_s desc;
#ifndef CONFIG_DISABLE_MOUNTPOINT
  FAR const char *relpath = NULL;
#endif
  bool isroot = false;
  int ret;

  /* If we are given 'nothing' then we will interpret this as
   * request for the root inode.
   */

  SETUP_SEARCH(&desc, path, false);

  inode_semtake();
  if (path == NULL || *path == '\0' || strcmp(path, "/") == 0)
    {
      inode   = g_root_inode;
      isroot  = true;
    }
  else
    {
      /* We don't know what to do with relative pathes */

      if (*path != '/')
        {
          ret = -ENOTDIR;
          goto errout_with_semaphore;
        }

      /* Find the node matching the path. */

      ret = inode_search(&desc);
      if (ret >= 0)
        {
          inode   = desc.node;
          DEBUGASSERT(inode != NULL);
#ifndef CONFIG_DISABLE_MOUNTPOINT
          relpath = desc.relpath;
#endif
        }
    }

  /* Did we get an inode? */

  if (inode == NULL)
    {
      /* Inode for 'path' does not exist. */

      ret = ENOTDIR;
      goto errout_with_semaphore;
    }

  /* Allocate a type DIR -- which is little more than an inode
   * container.
   */

  dir = (FAR struct fs_dirent_s *)kumm_zalloc(sizeof(struct fs_dirent_s));
  if (!dir)
    {
      /* Insufficient memory to complete the operation. */

      ret = ENOMEM;
      goto errout_with_semaphore;
    }

  /* Populate the DIR structure and return it to the caller.  The way that
   * we do this depends on whenever this is a "normal" pseudo-file-system
   * inode or a file system mountpoint.
   */

  dir->fd_position = 0;      /* This is the position in the read stream */

  /* First, handle the special case of the root inode.  This must be
   * special-cased here because the root inode might ALSO be a mountpoint.
   */

  if (isroot)
    {
      /* Whatever payload the root inode carries, the root inode is always
       * a directory inode in the pseudo-file system
       */

      open_pseudodir(inode, dir);
    }

  /* Is this a node in the pseudo filesystem? Or a mountpoint?  If the node
   * is the root (isroot == TRUE), then this is a special case.
   */

#ifndef CONFIG_DISABLE_MOUNTPOINT
  else if (INODE_IS_MOUNTPT(inode))
    {
      /* Yes, the node is a file system mountpoint */

      dir->fd_root = inode;  /* Save the inode where we start */

      /* Open the directory at the relative path */

      ret = open_mountpoint(inode, relpath, dir);
      if (ret != OK)
        {
           goto errout_with_direntry;
        }
    }
#endif
  else
    {
      /* The node is part of the root pseudo file system.  Does the inode
       * have a child? If so that the child would be the 'root' of a list
       * of nodes under the directory.
       */

      FAR struct inode *child = inode->i_child;
      if (child != NULL)
        {
          /* It looks we have a valid pseudo-filesystem directory node. */

          open_pseudodir(child, dir);
        }
      else if (!inode->u.i_ops)
        {
          /* This is a dangling node with no children and no operations. Set
           * up to enumerate an empty directory.
           */

          open_emptydir(dir);
        }
      else
        {
          ret = ENOTDIR;
          goto errout_with_direntry;
        }
    }

  RELEASE_SEARCH(&desc);
  inode_semgive();
  return ((FAR DIR *)dir);

  /* Nasty goto's make error handling simpler */

errout_with_direntry:
  kumm_free(dir);

errout_with_semaphore:
  RELEASE_SEARCH(&desc);
  inode_semgive();
  set_errno(ret);
  return NULL;
}